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Asked by to Daren, Lynne, Phillip, Simon on 18 Jun 2014. This question was also asked by .
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Lynne Thomas answered on 18 Jun 2014:
Crystals form when the atoms or molecules of a material turn into a solid. Most things that are solids are actually crystals including salt, sugar, minerals, diamond, paracetamol, the battery in your phone, silicon wafers that are used to make silicon chips. Most materials when you go from a gas to a liquid to a solid get smaller in terms of the volume that they occupy. The solid is the most efficient way you can put all the atoms and molecules together and when atoms and molecules are in a solid, they move around a lot less than when they are in a liquid or gas. It makes a grid in three dimensions much like a three-dimensional brick wall. You can make pretty much anything into a crystal if you try but things like the protein molecules are very difficult to make into crystals and the crystals of them tend to be very small!
Water is an interesting example of where the solid (ice) actually takes more volume than the liquid. Have you noticed this when you fill an ice cube tray with water and the ice cubes sometimes end up being bigger than the hole? This makes ice really fascinating and explains why we can ski, ice skate and toboggan. When you put pressure on the ice by standing on it, it squeezes it and makes it take up a smaller volume underneath you. Because the liquid takes up less volume it melts underneath you and that’s why you can slide on it! This is because of things called hydrogen bonds which hold the water molecules together.
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anon answered on 18 Jun 2014:
Crystals form when the molecules inside something arrange themselves in a really ordered way. Imagine you’ve got a box of k’nex – it doesn’t really look like anything other than a jumble of plastic, but when you start connecting the pieces together in grids and boxes you start to make something. Powders (or non crystals) form when the molecules are all higgldy piggldy, but crystals are when they stack nicely!
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Simon Redfern answered on 18 Jun 2014:
The atoms that make up crystals like to stick to each other in particular ways, and often this gives them a particular geometric structure – they want to bond with each other in particular directions. Because of this, when lots of them get together to form a solid from, say a liquid or gas of the same stuff, they tend to pack together in an orderly manner. It’s rather like lines of soldiers on the parade ground, or better still, stacks of oranges at the market place – they stack together regularly to form a crystal with an organised atomic structure.
Here’s a picture of an “orange crystal”:
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Daren Fearon answered on 18 Jun 2014:
Crystals form when molecules pack in a very specific and ordered way. Crystals can be made of billions of molecules all aligned the same way! Smaller molecules, like salts, tend to pack together better to give bigger crystals than bigger molecules like proteins which form very small crystals which you need a microscope to see. There is a picture of some protein crystals on my profile if you want a look!
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